What I’ve Learned Today:
I had always figured that ‘eject‘ and ‘umount‘ were the same thing in that they both unmounted a drive whether USB Thumb Drive or CD-ROM. This isn’t entirely true. ‘umount’ will simply unmount the partitions for the disk, ‘eject’ will unmount the partitions as well as unmount the boot volume. The first example that comes to mind is the CD-ROM drive. If you had simply tried to ‘umount /dev/cdrom0’, the CD-ROM partitions would be unmounted, but the CD would still be stuck in the tray. With the ‘eject’ command, the CD-ROM would be unmounted and the tray would physically eject the media.
There are some devices out there that mount a pseudo (fake) CD-ROM drive, like SanDisk U3, that may need to be ejected depending on your application.